1. Field of the Invention
This invention generally relates to thin-film transistors (TFTs), liquid crystal displays (LCDs), integrated circuit (IC) fabrication and, more particularly, to a TFT formed on a single-crystal semiconductor film that is laterally grown from a single-crystal seed crystal.
2. Description of the Related Art
Although high performance polycrystalline silicon (poly-Si) TFTs can be fabricated by conventional lateral crystallization technologies, the resulting devices, as expressed by absolute performance and distribution of characteristics, is still not sufficient to enable the fabrication of advanced circuits that offer low power consumption, high speed and other desirable characteristics. The main problem stems from the lack of uniformity between devices, which, in turn, is typically traced to the microstructure of the device active layer (poly-Si).
In the case of lateral crystallization, a laser annealing technique that currently offers improved device characteristics, the above-mentioned non-uniformity results from the (non-uniform) content of defects in the poly-Si layer formed during laser irradiation. Furthermore, the orientation of grains in the poly-Si layer is practically impossible to control with conventional irradiation techniques. If the orientation of grains in the film could be controlled, a very uniform and practically defect-free Si microstructure might be achieved. Devices build on such material would have a substantial advantage in performance and uniformity over the current state of the art. In fact, the film would practically be single-crystal-Si, and not poly-Si.
It would be advantageous if an annealing process could be devised that controlled the grain orientation of crystals in a significant region of semiconductor film.
It would be advantageous if TFTs could be fabricated in semiconductor film regions with a controlled, single-crystal orientation, to enhance the predictability of device performance.